Steam Turbine

ABSTRACT

A steam turbine ( 10 ), especially in the form of a double-flow low-pressure steam turbine, includes a rotor ( 11 ) which is rotatably mounted around an axis ( 21 ) and which is concentrically enclosed with a spacing by an inner casing ( 13 ), forming annular steam passages ( 28, 29 ), and which has a multiplicity of rotor blades ( 12 ) which project into the steam passages ( 28, 29 ), wherein the inner casing ( 13 ) supports a multiplicity of stator blades ( 12 ) which project into the steam passages ( 28, 29 ) and which, for feeding steam to the steam passages ( 28, 29 ), has an inlet duct ( 15 ) which is directed around the axis ( 21 ) and tapers in the flow cross section. With such a steam turbine, the production is simplified by the inner casing ( 13 ) being formed as a welded construction, in which blade carriers ( 14 ), which delimit the steam passages ( 28, 29 ) and are produced as cast parts, are welded to additional forged or rolled steel elements ( 20 ) for fastening the stator blades ( 12′ ).

This application claims priority under 35 U.S.C. § 119 to Swissapplication No. 00349/07, filed 2 Mar. 2007, the entirety of which isincorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the field of thermal machines, and moreparticularly to a steam turbine.

2. Brief Description of the Related Art

With large steam turbosets, as are described, for example, in thearticle by L. Busse et al., “World's highest capacity steam turbosetsfor the lignite-fired Lippendorf power station”, ABB review 6/1997, p.13-22 (1997), and are shown in FIG. 2 there, double-flow low-pressuresteam turbines are used, in which the steam is fed radially via acentral scroll-shaped inlet duct, and then flows out in both directionsthrough the steam passages which are formed between the rotor and theconcentric inner casing, and, expanding on the rotor blades of therotor, performs work. The inlet scroll is integrated into the innercasing, as well as a plurality of steam extraction chambers into whichsteam, at a specified pressure, can flow from the steam passages throughopenings in the inner casing, and be extracted. Furthermore, the innercasing, on the sides which delimit the steam passages, serves as acarrier for a multiplicity of fixed stator blades which project into thesteam passages.

With the known low-pressure steam turbines, the inner casing, with theinlet scroll and the steam extraction chambers, is divided along ahorizontal parting plane into an upper half and a lower half. The twohalves are produced in each case as one-piece cast parts, preferablyfrom nodular cast iron. This technique allows the production of largecastings with complicated shape (with inlet scroll, steam extractionchambers and exhaust diffuser) at low cost. The stator blade carriers inthis case are integrated into the inner casing.

With this solution, it is disadvantageous that such casings are verydifficult to produce. The number of manufacturers, therefore, is limitedand problems frequently occur. Also, it is difficult to repair suchcastings if problems occur during casting or during the subsequentmachining.

In the past, it has already been proposed (U.S. Pat. No. 1,483,995) toassemble a separate scroll casing for a turbine or pump from one or morecentral cast parts, which form a central stator blade ring, andplate-like steel elements, which, connected in an overlapping manner,form the scroll casing with the inlet opening. The parts of the device(the rotor) which are equipped with rotor blades, are not enclosed bythis casing. In particular, is it also not apparent how the associatedstator blades are to be fastened on a casing which encloses the rotor.

A low-pressure turbine section, which is designed in a multi-shell,entirely welded construction, is known from U.S. Pat. No. 3,594,095. Ascroll-shaped inlet duct in this case is not provided.

SUMMARY

One of numerous aspects of the invention, therefore, includes creating asteam turbine which addresses the disadvantages of known steam turbinesand which, in particular, includes an inner casing which can be moreeasily and more cost-effectively produced.

According to another, particularly advantageous aspect of the invention,the inner casing is formed as a welded construction, in which the bladecarriers, for fastening the stator blades, which blade carriers delimitthe steam passages and are produced as castings, are supported byadditional forged or rolled steel elements. Since the cast parts withthis solution are limited to the blade carriers and, therefore, areformed in a smaller and less complicated manner, fewer fabrication andrepair problems result. At the same time, radial and axial deformationsof the blade carriers are less than with an integrated cast casing, sothat narrower gaps at the blade tips, and therefore higher efficiency ofthe turbine, are possible.

According to another aspect of the invention, the inlet duct, whichtapers in the flow cross section, is formed as an inlet scroll.

Another aspect includes a plurality of steam extraction chambers formedin the inner casing, and the steam extraction chambers are formed ordelimited by the blade carriers and the steel elements which are weldedto them.

A further aspect of the invention includes that support rings, which arearranged concentrically to the axis with axial spacing and which supportthe blade carriers on their rear side, are provided for stiffening theinner casing, tie rods are provided between the support rings forabsorbing transverse forces, and the steel elements are welded to thesupport rings.

The tie rods can especially be welded or screwed to the support rings.

Furthermore, it is conceivable and advantageous that at least one radialguide vane is arranged in the inlet duct.

According to yet another aspect, the blade carriers consist of nodularcast iron or cast steel.

BRIEF DESCRIPTION OF THE FIGURES

The invention is to be subsequently explained in more detail based onexemplary embodiments in conjunction with the drawing. In the drawing:

FIG. 1 shows, in longitudinal section, a double-flow low-pressure steamturbine with its inner casing according to an exemplary embodiment ofthe invention, and

FIG. 2 shows the section along the center plane II-II in FIG. 1.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

In FIG. 1, a double-flow low-pressure steam turbine, with its innercasing according to an exemplary embodiment of the invention, isrepresented in longitudinal section. FIG. 2 shows the section of thisturbine in the center plane (plane II-II in FIG. 1). The steam turbine10 is constructed with its two flows mirror-symmetrical to a verticalcenter plane 30. It includes a rotor 11, which is rotatable around ahorizontal axis 21 and concentrically enclosed with a spacing by aninner casing 13. Outwards widening annular steam passages 28, 29 areformed between the rotor and the inner boundary wall of the innercasing, through which the steam, which is fed radially in the center,flows outwards and, expanding on the rotor blades 12 which are fastenedon the rotor 11, performs work.

Rows of fixed stator blades 12′, which are fastened on blade carriers 14on the root side, alternate with the rows of rotor blades 12. The bladecarriers 14 are cast parts and preferably are formed of nodular castiron or cast steel. They are a part of the inner casing 13 and form theboundary walls for the steam passages 28, 29. The inner casing 13 isaltogether formed as a welded construction, in which the blade carriers14 are supported on the outside in an axially movable manner by forgedor rolled steel elements 20, and are sealed by sealing elements. Thewelded plate-form steel elements 20 not only form a scroll-shaped inletduct or an inlet scroll 15 in the central section of the steam turbine,but also form a plurality of steam extraction chambers 16 on the twosides of the center plane 30.

The steel elements 20 do not bear directly on the blade carriers 14, butbear via support rings 18, which are arranged concentrically to the axis21 with axial spacing for stiffening the inner casing 13. Tie rods 17,which by their ends are fastened on the support rings 18, especiallyscrewed or welded, are provided between the support rings 18 forabsorbing transverse forces.

The scroll-shaped inlet duct 15 is delimited on the outside by a scrollcasing 24 which (on account of the splitting of the inner casing 13 inthe parting plane 25) is constructed from simple steel plates. At leastone radial guide vane 19, which serves for deflection of the steam whichflows in through the steam inlet 23, is arranged in the inlet duct 15.

The inner casing 13 is split in the horizontal parting plane 25. As wellas the outer casing 26, it is supported by a support construction 27which lies beneath it and which in turn bears upon the outer casing 22.

By the combination according to the invention of cast blade carriers andforged or rolled steel plates or steel elements which are welded to themfor forming the inner casing, which is provided with an integrated inletscroll and with integrated steam extraction chambers, significantsimplifications and facilitations result during production of thecasing, without the mechanical and thermal characteristics beingdisadvantageously altered.

LIST OF DESIGNATIONS

-   -   10 Steam turbine (low-pressure, double-flow)    -   11 Rotor    -   12 Rotor blade    -   12′ Stator blade    -   13 Inner casing    -   14 Blade carrier    -   15 Inlet scroll (inlet duct)    -   16 Steam extraction chamber    -   17 Tie rod    -   18 Support ring    -   19 Radial guide vane    -   20 Steel element (forged or rolled)    -   21 Axis    -   22 Outer casing    -   23 Steam inlet    -   24 Scroll casing    -   25 Parting plane    -   26 Outer casing    -   27 Support construction    -   28, 29 Steam passage    -   30 Center plane

While the invention has been described in detail with reference toexemplary embodiments thereof, it will be apparent to one skilled in theart that various changes can be made, and equivalents employed, withoutdeparting from the scope of the invention. The foregoing description ofthe preferred embodiments of the invention has been presented forpurposes of illustration and description. It is not intended to beexhaustive or to limit the invention to the precise form disclosed, andmodifications and variations are possible in light of the aboveteachings or may be acquired from practice of the invention. Theembodiments were chosen and described in order to explain the principlesof the invention and its practical application to enable one skilled inthe art to utilize the invention in various embodiments as are suited tothe particular use contemplated. It is intended that the scope of theinvention be defined by the claims appended hereto, and theirequivalents. The entirety of each of the aforementioned documents isincorporated by reference herein.

1. A steam turbine comprising: a rotor rotatably mounted around an axis;an inner casing which concentrically encloses the rotor with a spacing,the spacing forming annular steam passages; a multiplicity of rotorblades projecting into the steam passages; and a multiplicity of statorblades supported by the inner casing and projecting into the steampassages; wherein the inner casing includes an inlet duct for feedingsteam to the steam passages directed around the axis and tapers in theflow cross section; wherein the inner casing is a welded constructionand comprises cast blade carriers which delimit the steam passages, andadditional forged or rolled steel elements supporting the bladecarriers, for fastening the stator blades.
 2. The steam turbine asclaimed in claim 1, wherein the inlet duct, which tapers in the flowcross section, comprises an inlet scroll.
 3. The steam turbine asclaimed in claim 1, further comprising: a plurality of steam extractionchambers formed in the inner casing, and wherein the steam extractionchambers are formed or delimited by the blade carriers and the steelelements which are connected to them.
 4. The steam turbine as claimed inclaim 1, further comprising: support rings arranged concentrically tothe axis with axial spacing and supporting the blade carriers on theirrear side, the support rings stiffening the inner casing; tie rodsbetween the support rings configured and arranged to absorb transverseforces; and wherein the steel elements are welded to the support rings.5. The steam turbine as claimed in claim 4, wherein the tie rods arewelded or screwed to the support rings.
 6. The steam turbine as claimedin claim 1, further comprising: at least one radial guide vane arrangedin the inlet duct.
 7. The steam turbine as claimed in claim 1, whereinthe blade carriers are formed of nodular cast iron or cast steel.
 8. Thesteam turbine as claimed in claim 1, wherein the steam turbine is adouble-flow low-pressure steam turbine.